In conventional cellular wireless communications technologies, user equipment communicates with a base station by using an air interface, and the base station forwards user data to a destination node in a network.
With development of mobile communications technologies, to better satisfy a user requirement, and improve efficiency of information exchange between user equipments, a mechanism for direct communication between user equipments, that is, D2D communication (Device to Device Communication), which is also referred to as sidelink communication, is introduced to a Long Term Evolution (LTE for short) system. Different from the conventional cellular wireless communications technologies, data of user equipment is directly transmitted by using an air interface between user equipments without needing to be transmitted by using a base station; therefore, a network forwarding delay is reduced. In a D2D communication mode, a direct communications link between user equipments may be established under the control of or with the assistance of a network device, such as a base station. A typical application scenario of the D2D communication is a public safety scenario. For example, for communication between firefighters, a typical service type is a voice service.
As shown in FIG. 1, a D2D communications system includes a base station 101, user equipment (UE) 1, and UE 2. Cellular wireless communication may be performed between the base station 101 and the UE 1. D2D communication may be performed between the UE 1 and the UE 2.
Current D2D communication supports group communication, that is, one-to-many communication. D2D user equipment may send D2D data to user equipments of a communication group. As shown in FIG. 2, a base station 201 controls or assists UE 1, UE 2, UE 3, and UE 4 to establish D2D group communication. For example, a group 202 is a public safety group, and the UE 1 may directly transmit data to the UE 2, the UE 3, and the UE 4 without using the base station.
The current D2D communication also supports unicast communication, that is, one-to-one communication. D2D user equipment directly sends D2D data to another user equipment.
However, because a transmission resource is obtained by user equipment through contention, a current D2D communications system may have problems of insufficiently timely and reliable transmission of data, or the like because some user equipments cannot obtain resources through contention.
Because of an inherent disadvantage of a D2D communications manner in an existing wireless communications system, a novel D2D data transmission method and device are urgently needed in this field, so as to resolve the problems of insufficiently timely and reliable transmission of some data, or the like in the current D2D communications system.